1. Field of the Invention
The present invention relates to an epoxy resin composition and a hardened resin thereof, in more detail an epoxy resin composition using a heat latency polymerization catalyst and its hardened resin.
2. Background Art
Semiconductor light emitting devices, such as light emitting diode, LD (lazer diode) and the like, are small and emit light of vivid color efficiently. Moreover, since it is a semiconductor device, it does not burn out like a bulb. In addition, it has the feature of being excellent at driving characteristics and resistant to vibration and repetition of ON/OFF lighting. Therefore, it is used as various indicators or various light sources. As a material which shields such a semiconductor light emitting device, an epoxy resin is preferred to use from the point of a translucency, productivity, the ease of treating, etc. The epoxy resin hardened especially using an acid anhydride hardening agent has little discoloration by heat treatment, and is excellent at a translucency and light fastness. A hardening accelerator for promoting hardening is also used together in the epoxy resin composition using such an acid anhydride hardening agent.
As a hardening accelerator, a high heat-resistant phosphonium salt of halogen is used conventionally. However, such a halogen salt is not desirable because it becomes the cause of electrode corrosion especially under high temperature and high humidity. For solving this problem, tetraphenylphosphonium tetraphenylborate is developed as a hardening accelerator (for example, refer to JP-A 4-209624). However, tetraphenylphosphonium tetraphenylborate has bad mutual solubility with an acid anhydride hardening agent and an epoxy resin, and has the problem of becoming a cloudy hardened resin without a translucency when the epoxy resin composition compounded this tetraphenylphosphonium tetraphenylborate is hardened comparatively at low temperature.
Although in recent years, tetrabutylphosphonium tetraphenylborate is developed as a hardening accelerator in which the solubility has been improved (for example, refer to JP-A 2002-53644), heat resistance thereof is inferior to the conventional tetraphenylphosphonium tetraphenylborate, and therefore the development of catalyst having higher solubility and being excellent at heat resistance is desired.